1. Field of the Invention
The present invention relates to a stacker crane and a method for operating the same, and in particular relates to reducing stress between a mast and a lower frame.
2. Description of the Related Art
The applicant has proposed providing travel motors in upper and lower carriages of a stacker crane so as to cause the upper and lower carriages to travel in a synchronized manner (See, for example, JP 2002-106414A). If the upper and lower carriages run out of synchronization, a strong force is exerted on the connection between the mast and the carriages, and therefore, in JP 2002-106414A, the mast is attached pivotally to the lower carriage.
However, a pivotal mast is difficult to stand upright during installation of the stacker crane. Similarly, if the mast does not stand upright, it is difficult to perform maintenance on the stacker crane. Furthermore, if a mast with a large weight is to be pivoted, a large pivoting mechanism is needed.